The AM Forum

I'm going to be installing new parasitic suppressors in the Gonsets  a la Measures, but got questions about the kind of flux and solder i need - I know it's tin-silver, but whats the best ratio and what kinda flux is required?

Dynagrip #430 kit from All-State includes 4' of silver bearing solder and a small dropper bottle of Duzall liquid flux
Another company that makes a small kit is J W Harris out of Mason, Ohio
They even make kits to solder aluminum.
These kits can be purchased at nearly any welding supply store. They also work good for soldering the ends on SS motorcycle cables.

Do not try to silver solder the nichrome wire directly into the circuit--just tin it with the silver solder and then regular solder works FB to attach it to tie points or whatever.
Skip

ok skip thanks. I'll find a shop and get the goodies.

I am now treating the Gonsets as homebrew projects instead of resto jobs.

Why do you need nichrome wire to wind a parasitic choke?  I make mine by winding ordinary copper wire over carbon composition resistors.  The necessary circuit loss at VHF and UHF occurs in the resistor; the wire acts as an RF choke at the parasitic frequency, and as a dead short at the operating frequency.

I used to be able to find 5-watt and 10-watt carbon resistors for this purpose, but these days I use a bundle of one or more 2-watt resistors in parallel to give about 50 ohms.  I suppose a large one could be made using a series-parallel combination.

Some of my big transmitters use Glo-Bars for the resistor.  I have picked up a number of those over the years at hamfests and have an adequate supply on  hand.  The HF-300 rig uses a pair of commercially made parasitic suppressors (by Bud, IIRC, manufactured sometime about 1939).  It has a coil of #14 wire wound over what looks like an ordinary 10W wirewound resistor, but I  suspect the resistor is one of those special jobs wound so as to be approximately non-inductive.

it may be a bunch of hooey, but AG6K, Rich Measures, uses distributed resistance in the form of nichrome wire and MOF resistors
to make new parasitic suppressors that are supposed to lower the VHF Q of the anode circuit at vhf.  Don, (or anyone else in the brain trust) would you look at his stuff and see i you can come up with any holes or BS in his methods?

www.somis.org (http://www.somis.org)

I did yet more digging and the Gonset amps as made seem to be prone to parasitics because of poor tank design leading from a 5+ inch silver ribbon 1/2" wide leading from the plate choke ( which is undersized)  to the plate tuning cap, then another 5+ inches going from the bandswitch to the loading cap. Stories of burned up bandswitches are pretty common, enough to know that it's not just me.

I'm now treating these amps as homebrew kit projects and will settle to single band them for 75, 40, and 160. Ideal would be to make them settle down enough to where I could dual band or tri band them with a bandswitch. I don't care abut anything above 40 meters. In fact I am going to make them inoperative on any band above 40 by cutting the straps to the bandswitch for 20 15 and 10.
The GSB 101 and 201 are very similar circuits, so I'm posting the parts list and schizmatic for the 101 since it's very hi Q.  dont worry about the control circuits and such, I need to focus on the input - output, grid bypassing,tank design, etc. One thing Slab noticed is that they fed the B+ right through the same wiring harness that has the grid lead coming/going. I'm going to change that. Since the B+ lead comes within 2 inches of the cathode chokes/coils at one point, would a bypassed double shielded coax teflon B+ line help? The B+ is 1700+, doing this does not impress me as safe or good design.

of special interest: does this "neutralizing" scheme of feeding back out of phase from the anode to a reversed wound coil to ground over one cathode coil really work? Does it work at all frequencies, or can it lead to input-output positive feedback at VHF? What would you do to make this 40+ year old design more stable? What's the absolute best way of grounding the grids for both rf and dc?

I can't remember what brand of final tubes you have in your Gonset but by chance were they replaced with Svetlana?  There is a Svetlana application note about changes to prevent oscillation when used as replacements in a Yaesu FL-2100 series amp:  http://www.rfparts.com/technical.html

My GSB-201 Mk.IV (bought used a couple of years ago) has been operated on 80-10 without any fireworks so something odd has to be going on with your amps.

Rodger WQ9E

They're a rather odd set of west german made 811A's. I'm going to ditch them and put Cetron 572B's in when I get back home. I've done nothin but burn up bandswitches since I got it. It has a bad case of fireworks in that area. Maybe it's as simple as the tubes. My elmer had one of these amps and used it for years to chase DX with, so I know they do work. I'm just frustrated as shit with mine because it hasn't.

Hey, could you do me a flavor and peek inside the case of yours and see where the position of your neutralizing metal bracket is in relation to the tubes next to it? the one on mine has been changed. I'm curious to know if it's set exactly in the middle of the space between those tubes.

This is the best shot I could get through the case top (as you know these things are heavy and are a pain to take apart).  Let me know if you need a different angle.

I had to light it externally because the tubes create too much glare inside.  Probably the macro lens wasn't the best choice due to low depth of field but hopefully it gives you a pretty sharp view of the actual mounting orientation.

Do you have CR1 attached to the correct transformer terminal for the tubes in use?  A note was added to later schematics about this change and it should on Terminal 17 for 811A and Terminal 16 for 572B for proper bias.

Rodger WQ9E

thats a good enough photo for the purpose, thank you !  :D

I will attempt to position mine as exactly as I can to match yours.

yes, I've had CR1 always on term 17. Have not tried it with the 572B's yet. Going home today for 1 day, so I can work on it tonight some.

You are welcome and good luck, it really should work properly so something is up with yours and I hope you find it without too much more difficulty!

As to nichrome wire for parasitic suppressors, I have a number of amplifiers using various tubes including an SB-220 I built from a kit in 1976 and none of them use anything but the standard parasitic suppressors and I have never had any problems.

If you go to the searchable archives of the Amps mailing list at contesting.com:  http://lists.contesting.com/archives//html/Amps/  you will find lots of "discussion" on the Measures suppressors.

 

Rodge said:
Yeah, well that "discussion" board has been dominated by W8JI and his band of merry men. I've never met Rich Measures, but in the short time I've known him, he has been able to back up everything he claims with facts and figures. W8JI is still trying to figure out AC circuit basics. Plus, I've seen the nichrome parasitic suppressors work first hand in an amplifier. Where the standard 47Ω resistor with a 4~5 turns of #10 wire wrapped around it were installed, replaced by nichrome and re-installed that proved that the old style suppressors were the bane of the oscillations. You can do what you want, but I saw with my own two eyes that nichrome works as advertised in an A/B test.

I'm going to go with the nichrome. I am aware of the running feud between JI and Measures but i've done plenty of reading and I think Measures is right.

somewhere in that running discussion is a thread on the Gonset amps being prone to arcing due to poor tank design layout resulting in long anode lead length. I got the nichrome today,  30 ft of 22 gauge for 6 bucks. I got all the other parts in too.

I'll be using new nichrome suppressors, the double staggered nichrome anode connections, a few vhf >30 to 200 mhz ferrite beads, and rerouting the HV feed out of the main wiring harness (to it's own ceramic feed thru) as well as new grid bypasses using silver micas....and a cathode rf resistor or 2. I wish I had a better plate choke but I'll try the stock one.

hopefully, we'll turn it on, load it up into the termaline, and do nothin but make power this time with no fireworks.